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9.1 State THREE factors that have an effect on shrinkage in a welded joint - NSC Mechanical Technology Welding and Metalwork - Question 9 - 2023 - Paper 1
Question 9
9.1 State THREE factors that have an effect on shrinkage in a welded joint. 9.2 Explain what peening is. 9.3 Name TWO types of strungbacks used to control distorti... show full transcript
Worked Solution & Example Answer:9.1 State THREE factors that have an effect on shrinkage in a welded joint - NSC Mechanical Technology Welding and Metalwork - Question 9 - 2023 - Paper 1
Step 1
State THREE factors that have an effect on shrinkage in a welded joint.
Answer
Several factors can lead to shrinkage in a welded joint, including:
- Electrode Type: The type of electrode used can influence the amount of heat input and therefore the cooling rate.
- Welding Current: Higher welding currents tend to produce more heat, which can impact the amount of shrinkage observed.
- Flame Speed: The speed of the flame affects the heat distribution and can contribute to differential cooling and shrinkage.
Step 2
Explain what peening is.
Answer
Peening is a technique used in welding to counteract the shrinkage forces of a weld bead as it cools. This process involves hammering the weld area immediately after it is completed, which helps to strengthen the joint and reduce residual stresses by introducing compressive stresses into the surface of the weld.
Step 3
Name TWO types of strungbacks used to control distortion during the butt welding of plates.
Answer
Two types of strungbacks that can be utilized to control distortion are:
- Clips: These are mechanical devices that hold the plates in position to prevent warping during the welding process.
- Yokes: Yokes are structural supports that help maintain alignment and minimize distortion by applying direct forces against the plates being welded.
Step 4
Describe the effect of hot working on steel.
Answer
Hot working involves deforming steel at elevated temperatures, which affects its mechanical properties. As a result:
- Deformation and Recrystallization: These occur simultaneously, enabling the material to soften and become more workable.
- Grain Structure: Hot working generally leads to a finer grain structure, improving the ductility and overall properties of the steel, provided the temperature is controlled above the recrystallization temperature.
Step 5
State THREE factors causing residual stress in welds.
Answer
Residual stresses in welds can be attributed to multiple factors including:
- Heat Present in the Weld: The localized heating and cooling during welding create thermal gradients that induce stress.
- Quality of Parent Metal: Variations in the properties of the base materials can lead to uneven expansion and contraction during welding.
- Welding Method Used: Different welding techniques can influence the amount of residual stress due to variations in heat accumulation and cooling rates.
Step 6
Identify the types of distortions shown in FIGURES 9.6.1 and 9.6.2.
Answer
In the given figures:
- Figure 9.6.1 illustrates Longitudinal Distortion, which typically involves elongation along the length of the welded joint.
- Figure 9.6.2 depicts Angular Distortion, characterized by a change in the angle between the connected parts, often resulting from unequal thermal contraction.
Step 7
State THREE effects of the rate of cooling on a welded joint.
Answer
The rate of cooling can significantly affect a welded joint in several ways:
- Distortion: Rapid cooling can lead to greater distortion due to uneven contraction in different parts of the weld.
- Mechanical Properties: Slower cooling rates can promote better mechanical properties by allowing for more uniform microstructure, while fast cooling can lead to brittleness.
- Internal Stresses: Varying cooling rates can cause internal stresses, making the welded joint more prone to cracking.